A conventional wireless communication apparatus such as a cellular phone, automobile phone and the like, for use in a wireless communication system includes a receiving antenna 1 connected to a receiver 5 and a transmitting antenna 11 connected to a transmitter 6, as shown in FIG. 25.
In the thus configured wireless communication apparatus, the reception signal is received via antenna 1 and input to receiver 5 while a transmission signal is output from transmitter 6 and radiated externally from antenna 11.
Generally, in most cases, the receiving antenna and transmitting antenna are integrated into one structure (designated at 1 in FIG. 26) and the signal transmission path is branched by a duplexer (DUP) 4 into two paths toward receiver 5 and toward a transmitter 6, as shown in FIG. 26. As another typical configuration, an active antenna changer switch 3 may be used to perform switching between an external antenna terminal 7 and antenna 1, as shown in FIG. 27.
In a conventional wireless communication apparatus having the configuration as shown in FIG. 25, when an interference signal corresponding to Δf=|frx±ftx| is input to antenna 1 where the reception frequency is represented as frx and transmission frequency is represented as ftx, jamming waves having a frequency equal to the reception frequency frx are generated by modulation between transmission frequency ftx and interference frequency Δf, in the active elements included in receiver 5 or transmitter 6. Therefore, the wireless communication apparatus has suffered the problem of its reception characteristics being deteriorated by the jamming waves.
In a conventional wireless communication apparatus having a configuration shown in FIG. 26, the level of the signal of transmission frequency ftx entering from transmitter 6 to receiver 5 is markedly high, so that the level of interference frequency Δf becomes further increased. As a result, the wireless communication apparatus has suffered the problem of its reception characteristics being further degraded.
When an external antenna is used, an antenna changer switch is used as disclosed in Japanese Patent Application Laid-open Hei 6 No. 37668. In the conventional wireless communication apparatus employing an active antenna changer switch 3 as the antenna changer switch as shown in FIG. 27, modulation between transmission frequency ftx and interference frequency Δf produces jamming waves having a frequency equal to the reception frequency frx. Accordingly, the wireless communication apparatus has suffered the problem of its reception characteristics being deteriorated by the jamming waves.
The present invention has been proposed in view of the above problems, it is therefore an object of the present invention to provide a wireless communication apparatus which performs communication using the reception and transmission frequencies, simultaneously, wherein degradation of its reception characteristics due to interference signals is prevented.